1. Field of the Invention
The present invention relates to a novel open cell body made of hard vinyl chloride resin used for purposes, such as duct pipes, aeration pipes, pits for surface dewatering, various air filters, solid-gas separating plates, solid-liquid separating plates, mother materials of deodorizers, and carriers of aromatics.
2. Description of Background and Material Information
Conventionally, open cell bodies made of synthetic resins, and flexible urethan foams obtained by the reaction of saturated polyesters or polyethers with isocyanate have become popular. Moreover, PVA sponges obtained by adding .alpha.-starch powders to polyvinyl alcohols as a foaming agent to formalize it and then flowing out the resulting product with water are also well known.
Related to this, open cell bodies made of vinyl chloride resins are disclosed in the inventions of Japanese Patent Publication No. 21898/1978, U.S. Pat. No. 4,226,943, Japanese patent application OPI Nos. 137930/1980 (Japanese Patent Publication No. 50662/1983), 90841/1981 (Japanese Patent Publication No. 25369/1983), and 14630/1982 (Japanese Patent Publication No. 58370/1983).
Jap. Pat. Pub. No. 21898/1978 and U.S. Pat. No. 4,226,943, both of which were filed by Otsuka Chemical Pharmaceuticals Co., Ltd., disclose "a method for producing an open cell body by molding a mixture containing at least one kind of vinyl chloride emulsified homopolymers and vinyl chloride emulsified copolymers, a plasticizer, and a blowing agent into a sheet followed by heating, which is characterized by adding at least one kind of wax which is selected from paraffin waxes having 20-80 carbon atoms and ester waxes having 20-80 carbon atoms consisting of monohydric and polyhydric alcohol esters of higher fatty-basic acid and also having substantially no compatibility with the vinyl chloride polymer to the mixture to obtain the open cell body" (Jap. Pat. Pub. No. 21898/1978), and also "a process for producing an open cell sheet made of a vinyl chloride resin which involves molding a foaming vinyl chloride resin composition into a sheet and heating the sheet to the temperature of decomposition of the blowing agent in the sheet or more, wherein the foaming vinyl chloride resin composition consisting of:
(1) a vinyl chloride resin of 100 PHR, PA0 (2) a plasticizer of 30-150 PHR, PA0 (3) a synthetic hydrogen carbonate wax of 1-8 PHR: a product produced in a step selected from the group consisting of depolymerization of polyethylene, polymerization of ethylene, and Fischer-Tropsch synthesis of coal gas, which has a molecular weight of 1500-7000, a softening point of 90.degree.-135.degree. C., and a grain size of 10-100 microns, PA0 (4) an alkali metal-Zn stabilizer of 1-5 PHR, and PA0 (5) a decomposing type organic blowing agent of 2-10 PHR, which contains at least 60% of azodicarbonamide" (claim 10 of U.S. Pat. No. 4,226,943). PA0 .circle.1 A vinyl chloride resin by emulsion polymerization is employed. PA0 .circle.2 The resultant product is a soft product containing a large quantity of a plasticizer therein. PA0 .circle.3 A thermal decomposing type blowing agent is employed. PA0 .circle.4 As essential components, (1) waxes are added (Jap. Pat. Pub. No. 21898/1978), (2) waxes and an alkali metal-Zn stabilizer are added. PA0 .circle.5 Other necessary components are added to make a paste paint. PA0 .circle.6 The resultant paint is applied on the base material, which is gellated to process into a sheet. PA0 .circle.7 The sheet is foamed by heating in a foaming furnace to produce an open cell body. PA0 (1) A sheet material is first formed using a calender technique (or an extruding technique) as processing method, followed by heating again in a foaming furnace to produce a foamed sheet. PA0 (2) A resin formed by a suspension polymerization method is used as the vinyl chloride resin (a paste grade product is used only in Jap. Pat. Appln. OPI No. 137930/1980). PA0 (3) The resultant product is a soft product containing 55-80 PHR of a plasticizer. PA0 (4) A mixture or composite stabilizer of stabilizers containing the group I metal in the periodic table and the group II metal in the periodic table is used as the stabilizer. PA0 (5) A surface active agent is added. PA0 1. a vinyl chloride resin formed by a suspension polymerization method or a block polymerization method. PA0 2. an ultramacromolecular weight acrylic processing aid, PA0 3. a mixture an organic stabilizer containing a metal of the group I in the periodic table and an organic stabilizer containing a metal of the group II in the periodic table, or a mixture of an organic composite stabilizer containing both metals, PA0 4. a mixture of an anionic surface active agent and a nonionic surface active agent, or a mixture of an anionic surface active agent and a low polymerization degree polyolefin or waxes, PA0 5. a thermal decomposing type organic blowing agent, such as azodicarbonamide, and PA0 6. as occasion demands, a powderly filler, such as calcium carbonate. PA0 .circle.1 those based on butadiene resins, such as ABS and MBS; PA0 .circle.2 those based on olefin resins such as PE, CPE, and EVA; PA0 .circle.3 those based on acrylate (RA) or methacrylate (RMA) resins; PA0 .circle.4 those based on condensation type resins; and PA0 .circle.5 others. PA0 (1) Improvement in surface gross; PA0 (2) Reduction in torque of the extruder; PA0 (3) Prevention of retentative degradation; PA0 (4) Prevention of draw down; PA0 (5) Increase in hot melt strength; and PA0 (6) Increase in discharge amount.
Although the latter invention does not specify that the vinyl chloride resin is an emulsified polymer, the use of a vinyl chloride resin "produced by emulsion polymerization" is clearly defined in the specification thereof, so that the vinyl chloride resin in the latter invention is an open cell body by means of an application method using the same emulsified polymer resin as in the former. The inventions described in these Jap. Pat. Pub. No. 21898/1978 and U.S. Pat. No. 4,226,943 can be summarized as follows:
The inventions of Jap. Pat. Appln. OPI Nos. 137930/1980 (Jap. Pat. Pub. No. 50662/1983), 90841 (Jap. Pat. Pub. No. 25369/1983), and 14630/1982 (Jap. Pat. Pub. No. 58370/1983) were developed by the inventors of the present invention (the latter two) and constitutes the basis of the present invention.
The invention of Jap. Pat. Appln. OPI No. 137930 (Jap. Pat. Pub. No. 50662/1983) is directed to "a process for producing an open cell body characterized by kneading with heating a substance compounded by adding a plasticizer, a mixed or composite stabilizer, in which an organic stabilizer containing a metal of the group I in the periodic table and an organic stabilizer containing zinc and other metals are combined, a thermal decomposing type chemical blowing agent powder, such as azodicarbonamide generally used as a blowing agent to form closed cells, and, as occasion demands, other compounding agents, to a vinyl chloride resin generally used for plastisol, (ii) rolling the resulting substance into a sheet by means of a calender method or an extrusion method, and then (iii) heating said sheet to a temperature sufficient to decompose the blowing agent".
The invention of Jap. Pat. Appln. OPI No. 90841/1981 (Jap. Pat. Pub. No. 25369/1983) is directed to "a process for producing an open cell body characterized by (i) kneading with heating a compounded substance which contains a widely used vinyl chloride resin produced by a suspension polymerization method as the main component a followed by (ii) adding the combination of an organic stabilizer containing a metal of the group I in the periodic table and an organic stabilizer containing a metal of the group II in the periodic table, or an organic stabilizer containing both of the group I metal and the group II metal in the same table, and a surface active agent selected from the group consisting of the combination of an anionic surface active agent and a nonionic surface active agent, and combination of an anionic surface active agent and a low polymerization degree polyolefin or waxes, a plasticizer, a thermal decomposing blowing agent, such as azodicarbonamide generally used for production of closed cell body, and, as occasion demands, other compounding agents, such as a filler to the vinyl chloride resin, (iii) rolling it into a sheet by means of a calender method or an extrusion method, and then (iv) heating and foaming said sheet by passing it through a foaming furnace".
The invention of Jap. Pat. Appln. OPI No. 14630/1982 (Jap. Pat. Pub. No. 58370/1983) is directed to "a process for producing an open cell body characterized by (i) kneading with heating a compounded substance in which 4,4'-oxybis(benzenehydrazide) as a blowing agent and an anionic surface active agent are added to a vinyl chloride composition (containing a vinyl chloride resin, a plasticizer, a stabilizer, a filler, and the like) to mold it into a sheet, and then (iii) foaming said sheet by heating."
The technical idea common to these three inventions is summarized as follows. Namely, it can be divided under five headings:
The products of these inventions are suitable for the uses, such as trim materials of car and upholstry covering materials, so that many of them are laminated with lining fabrics, such as knitted fabrics, plain fabrics, and nonwoven fabrics. These inventions, including the above Jap. Pat. Pub. 21898/1983 and U.S. Pat. No. 4,226,943 are extremely effective for such purposes, but could never be applied to production of the hard products, particularly, pipe-form products and plate products.
In the open cell hard products, for example a large quantity of the plasticizer should not be used, and if it is added (the purpose of the addition of the plasticizer is to act as processing aid so as to make the extrusion processing easy, and softening is not intended), the amount is as relatively small, i.e., 10-15 PHR. Accordingly, the thermal and kneading behaviors of hard products are quite different from those of the soft products.
The pipes or plate products are produced by extrusion techniques, but in this case, continuous foaming must be caused at a point in time when the product passes through an extruding die, and thus a method to obtain open cell bodies by first processing the vinyl chloride into a sheet by a calendering and then foaming the sheet by heating again, as in the conventional method, can not be applied. Therefore, in producing the hard open cell product, the steps of gellating and fusing the resin by heating and kneading in the extruder, at the same time decomposing and gasifying the blowing agent, simultaneously foaming the product as it passes through the extruding die, and forming the foam into an open cell body are required. The requirement for the steps can be achieved only by a completely novel technical idea which has never been found in the above conventional inventions and the purpose of the present invention lies in this point.